1. Field of the Invention
The present invention relates in general to an on-board DSRC (Dedicated Short-Range Communication) apparatus for use in an ETC (Electronic Toll Collection) system or the like of an ITS (Intelligent Transport System), and more particularly to an on-board DSRC apparatus in which the degree of freedom in installing an antenna unit and a body of the on-board DSRC apparatus is improved.
2. Description of the Related Art
In general, in an on-board DSRC apparatus for use in an ETC system or the like, in order that the communication between the on-board DSRC apparatus and the associated one of on-road communication machines for charge collection may be efficiently carried out, the position where an antenna unit is installed is limited to a dash board or the like of a vehicle.
On the other hand, since a body of the on-board DSRC apparatus may be installed in an arbitrary position of a vehicle in dependence on the convenience of a user, there is two cases, i.e., one case where the body of the on-board DSRC apparatus is constructed integrally with the antenna unit and the other case where the body of the on-board DSRC apparatus is connected to the antenna unit through a cable laid therebetween. From the foregoing, as for the types of the conventional on-board DSRC apparatuses, there are present a two-piece type in which the body of the on-board DSRC apparatus is constructed integrally with the antenna unit (in general, referred to as xe2x80x9cthe two-piece typexe2x80x9d in order to distinguish between the integral one-piece part and an external storage medium which is connected to the body of the on-board DSRC apparatus), and a three-piece type in which the body of the on-board DSRC apparatus is constructed separately from the antenna unit.
There is no wide application between the above-mentioned two types of on-board DSRC apparatuses. Therefore, after a user once has selected and purchased the associated one of the two types of on-board DSRC apparatuses, in the case where the installation of the body of the on-board DSRC apparatus, for example, is changed, even when the user intends to change the type of the on-board DSRC apparatus from the two-piece type over to the three-piece type, the specification thereof can not be changed at all.
Therefore, in the case where the change request made by a user occurs, there is no way except that the three-piece type of on-board DSRC apparatus is newly repurchased.
As for an example in which the change request made by a user occurs, there is the case where after a user has purchased the three-piece type of on-board DSRC apparatus and installed it to a vehicle, he/she repurchases a new vehicle to find that the three-piece type of on-board DSRC apparatus is excellent in the field of vision and also does not spoil the appearance of the interior of a vehicle, as compared with the two-piece type of on-board DSRC apparatus. In such a case, the on-board DSRC apparatus is desirable in which the type may be changed from the two-piece type over to the three-piece type.
However, when the type of the on-board DSRC apparatus is intended to be simply changed from the three-piece type over to the two-piece type (or from the two-piece type over to the three-piece type), the cable becomes unnecessary (or newly necessary), but the communication characteristics of the on-board DSRC apparatus changes as follows in dependence on the presence or absence of the cable.
In general, the cable for high-frequency transmission has the loss inherent therein and hence the presence or absence of the cable leads to the presence or absence of the loss.
For example, in the case of the three-piece type of on-board DSRC apparatus, in general, the correction needs to be carried out for the cable loss in the circuit characteristics of the body of the on-board DSRC apparatus.
In general, the cable loss in the vicinity of the frequency of 6 GHz is in the range of about 1.0 dB to about 2.0 dB per meter. Thus, assuming that the cable length is 3 m for example, the cable loss of 3 dB to 6 dB occurs.
The above-mentioned loss amount is related to the communication area between the on-board DSRC apparatus and the associated one of the on-road communication machines for charge collection, and hence the presence or absence of the cable exerts an influence on the spreading or reducing of the communication area.
In particular, in the case where the high-frequency wave is employed as the carrier wave as in the on-board DSRC apparatus, since the cable loss is large and also the fluctuation of the sensitivity and the transmission output due to the change of the type of the on-board DSRC apparatus (i.e., the presence or absence of the cable) is large, the type can not be changed only by simply removing or adding the cable therefrom or thereto.
As described above, in the conventional on-board DSRC apparatus, since the two types of products are separately handled, in order to change the type of the on-board DSRC apparatus from one type over to the other type, it is necessary to repurchase a new type of on-board DSRC apparatus. This is a problem associated with the prior art.
In addition, when the type of the on-board DSRC apparatus is intended to be charged from one type over to the other type only by removing or adding the cable therefrom or thereto, since the fluctuation of the sensitivity and the transmission output in change of the type is large, the communication area is changed. Thus, in the end, the type of the on-board DSRC apparatus can not be changed. This is another problem associated with the prior art.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide an on-board DSRC apparatus, having the high degree of freedom of installation of an antenna unit and a body of the on-board DSRC apparatus, in which the fluctuation of the cable loss due to the presence or absence of a cable is automatically switched and corrected on the on-board DSRC apparatus body side, thereby being able to cope readily with the repurchase of a vehicle or the change due to the preference of a user while maintaining a communication area fixed before and after having changed the type of the onboard DSRC apparatus from one type over to the other type.
According to one aspect of the present invention, there is provided an on-board DSRC apparatus comprising
an antenna unit mounted on a vehicle, and
a body of the on-board DSRC apparatus mounted on the vehicle to be connected to the antenna unit, the body including a transmission and reception units associated with the antenna unit to communicate with the associated one of on-road communication machines that is installed on a travelling road for the vehicle,
xe2x80x83in which
the body of the on-board DSRC apparatus comprises
switch means for operating in response to the presence or absence of a cable which is selectively inserted between the antenna unit and the body of the on-board DSRC apparatus, and
changing means for changing the attenuation amount of the transmission and reception units in response to the operation of the switch means, and in which
the changing means corrects the attenuation amount in such a way as to compensate for the fluctuation of the cable loss due to the presence or absence of the cable.
According to another aspect of the present invention, there is provided an on-board DSRC apparatus in which the switch means is constituted of:
a projecting part which is provided on the surface side of the antenna unit facing the body of the on-board DSRC apparatus;
a recess part which is provided on the surface side of the body of the on-board DSRC apparatus facing the antenna unit;
and an opening and closing switch which is turned on by inserting the projecting part into the recess part.
According to still another aspect of the present invention, there is provided an on-board DSRC apparatus in which
the switch means is constituted of
a magnet member which is provided on the surface side of the antenna unit facing the body of the on-board DSRC apparatus, and
a magnetic switch which is provided on the surface side of the body of the on-board DSRC apparatus facing the antenna unit and which is turned on by making the magnet member come close to the magnetic switch.
According to yet another aspect of the present invention, there is provided an on-board DSRC apparatus in which
the changing means is constituted of
a control unit which is operated by turning on the switch means, and
a variable attenuator for carrying out the correction in such a way as to increase the attenuation amount of the transmission and reception units in response to the drive by the control unit.
In addition, according to yet another aspect of the present invention, there is provided an on-board DSRC apparatus in which
the changing means is constituted of
high-frequency switches for carrying out the change operation in conjunction with the on operation of the switch means, and
a fixed attenuator which is selectively connected to the transmission and reception units through the high-frequency switches.
Also, according to yet another aspect of the present invention, there is provided an on-board DSRC apparatus in which
the body of the on-board DSRC apparatus includes
a controller of the on-board DSRC apparatus for processing communication information which has been transmitted and received through the transmission and reception units, and
a storage medium insertion unit into which an external storage medium is inserted to and from which the information relating to the charge collection is transmitted and received through the controller of the on-board DSRC apparatus, and in which
the body exchanges the information relating to the charge collection with the associated one of on-road communication machines for charge collection which is installed on a toll road for the vehicle, and automatically carries out the charge collection on the basis of the information relating to the charge collection.